The present invention is related to a transmission system for transmitting a multiplex signal from a transmitter to a receiver, said multiplex signal comprising at least one information section carrying information about the multiplex signal, the receiver comprising evaluation means for evaluating said information section, said evaluation means being arranged to select information sections with symbol values corresponding to a predetermined sequence of symbol values, the receiver further comprises processing means for processing the multiplex signal in dependence on information present in the selected information sections.
The present invention is also related to a receiver, a decoder, a transmission method, a receiving method and a decoding method for use with such a transmission system.
A transmission system according to the preamble is known from the MPEG-2, DVB, JSAT Transport Demultiplexer, Preliminary Technical Manual published by LSI Logic under document number DB14-000007, Draft Jul. 30, 1996, pp. 4-12-4-15.
Digital broadcast systems as they are being standardized, or are already standardized are based on the so-called MPEG-2 transport stream. The MPEG-2 transport stream offers the possibility of transporting digital video signals and other signals, such as related audio or data signals associated therewith in a very flexible way. The MPEG-2 transport stream is based on 188 byte transport packets, which carry a plurality of so-called elementary streams. Each of said elementary streams is identified by a so-called Packet ID (PID). This elementary streams can be (encoded) video streams, audio streams, and related data signals as required for functions like conditional access or electronic program guides (EPG,s).
The relation between a program and the corresponding elementary streams is defined by a plurality of tables. First there is the Program Map Table (PMT) in which the relation between each program in the transport stream and the PID of the related audio and video signals is stored. Second, there is the Program Association Table (PAT) in which the number of programs transported by the transport stream is stored. Further the PAT gives for each of the programs the PID of the elementary stream which carries the entries of the Program Map Table. Finally there is the Conditional Access Table (CAT) which holds the relation between the different types of conditional systems that may be used and the combination of conditional access PID's, table ID's and table ID's associated therewith.
These tables are stored in the receiver and are initialized and updated by information carried by the information sections. These information sections are also identified by a PID. The PID for the PAT is "00", and the PID for the CAT is "10". The PID for the PMT is stored in the PAT at the position corresponding to the program actually to be decoded.
When a program with number i has to be decoded, the PMT table has to be reconstructed from the transport stream. The decoder reads from the Program Association Table the PID for program number i. Using said PID, all elements of the PMT are read from the transport stream, and the complete PMT is built up using said elements. If the PMT is constructed, the demultiplexer can find the elementary streams in the multiplex signal.
Sometimes during a transmission of a multiplex signal the PMT has to be updated due to a change of said multiplex signal. This can be caused by the addition of programs and/or elementary streams. This change is indicated by a changed version number of the Program Association Table entries. In order to be able to find PAT entries of which the version number has changed, the receiver must perform a filtering operation to distinguish between all possible version numbers. Because 5 bits are reserved for the version number of the PAT, 32 different version numbers are possible. This requires 32 filter operations for each PAT entry, resulting in a substantial computational effort.